1. Field of the Invention
The present invention relates to a multiple disc clutch apparatus which is used in an automatic transmission or the like, for a car, and particularly to the technology for facilitating the manufacture thereof or enhancing the cooling performance.
2. Related Background Art
Generally, an automatic transmission of a car is provided with a planetary transmission mechanism of three to five speeds, in addition to a torque converter serving as a fluid coupling, and effects transmission by properly fixing or releasing the constituent elements (a sun gear, a planetary gear, etc.) of the planetary transmission mechanism by means of a clutch or a brake. A clutch and a brake of a wet-type multiple disc type in which friction plates and separator plates are alternately provided, are employed as the clutch and the brake to be assembled in the automatic transmission, except in some band-type brakes. A pressure oil from a transmission control hydraulic circuit is used in pressure contact (frictional engagement) of the plates of the two types. Also, since a comparatively large torque capacity can be obtained with a small volume and a smooth connection can be easily performed in an automatic two-wheeled vehicle, a wet-type multiple disc clutch is used as a clutch for intermitting the driving force.
FIG. 15 is a longitudinally cross-sectional view of the essential part of a conventional wet-type multiple disc clutch. As shown in this drawing, in this wet-type multiple disc clutch 1, externally splined friction (brake) plates 21 are brought into spline-fitting with the inner peripheral surface of a clutch case 3 to be slidable while internally splined friction plates 41 are brought into spline-fitting with the outer peripheral surface of a hub 5 to be slidable. Frictional materials 55, 75 are bonded to frictional material bonding surfaces 53, 73 of the respective friction plates 23, 41. When an automatic transmission pressure oil is introduced into an oil chamber 13 of the clutch case 3, a piston 9 which is fitted in a cylinder 7 moves to the left in the drawing and the both friction plates 23, 41 are contacted with each other with pressure, so that the clutch case 3 and the hub 5 are connected together. In FIG. 15, referential numerals 63 and 83 denotes frictional surfaces of the friction plates 21, 41, respectively.
In the conventional wet-type multiple disc clutch 1, one of the surfaces of each of the friction plates 21, 41 becomes the frictional material bonding surface 53 or 73, and the other becomes the frictional surface 63 or 83. Because of this arrangement, various problems as described below will occur. For example, it is desirable that the frictional material bonding surfaces 53, 73 be comparatively rough so as to enhance the bonding strength with the frictional materials 55, 75. Meanwhile, it is desirable that the frictional surfaces 63, 83 be smooth so as to suppress friction of the frictional materials 55, 75 which are in slide contact therewith. However, of each of the friction plates 21 and 41, if one of the surfaces is processed to have a surface roughness different from that of the other, the processing process and the processing devices become inevitably complicated, which inevitably brings about an increase in the manufacturing cost and the equipment cost, and lowered mass productivity. When an adhesive for bonding the frictional materials 55, 75 adheres to the frictional surfaces 63, 83, there arises an undesirable possibility that the sliding contact of the frictional surfaces 68, 83 with the frictional materials 55, 75 can not be conducted smoothly. As a result, it becomes necessary to take such means or a special bonding step as preventing the adhesive from adhering to the frictional surfaces 63, 83.
On the other hand, when the wet-type multiple disc clutch 1 is coupled or engaged, the frictional material 75 of each internally splined friction plate 41 is brought into sliding contact with the frictional surface 63 of the corresponding externally splined friction plate 21 and the frictional material 55 of each externally splined friction plate 21 is brought into sliding contact with the corresponding frictional surface 83 of the internally splined friction plate 41, so that a temperature rise of the both friction plates 21, 41 is inevitable due to the frictional heat. This temperature rise often occurs locally since the frictional materials 55, 75 bonded to the frictional material bonding surfaces 53, 73 are heat insulating materials, so that thermal deformation such as scorch or warp is easily created on the both frictional plates 21, 41.